The control of polyphosphate (polyP) metabolism will be studied in Helicobacter pylori (Hp), a fastidious microaerobic pathogen implicated in peptic ulcer disease and gastric cancer. PolyP is a long chain polymer of hundreds of phosphate residues linked by high-energy phosphoanydride bonds. Studies using fast growing species (e.g., E. coli, P. aeruginosa; quite unlike Hp in physiology) indicate that polyP is needed for traits such as stress resistance, motility and virulence; and that polyP is made by polyphosphate kinases (PPK), and consumed by PPK or an exopolyphosphatase (PPX). Hp is one of the most genetically diverse of bacterial species. Some of Hp's diversity is postulated to affect important quantitative phenotypic traits that might be seen in studies of metabolic genes. Our initial results indicate that (i) the ppk1gene is essential for some Hp strains, but not others; and (ii) in strains for which ppk1 is dispensable, ppk1 inactivation can block or impair growth in mice. The proposed studies have two specific aims. First: To better understand roles of ppk1 and polyP in Hp, and diversity among Hp strains in these roles. Here we will further test the inferred essentiality of ppk1 in certain Hp strains; select for genes or mutant alleles that at least partially compensate for ppk1 inactivation; and study the interplay between exopolyphosphatase (PPX) and PPK1. Second: To learn if the need for PPK1 or polyP in vivo depends on host genotype or physiology, and if PPK1 is needed primarily to establish, or also to maintain, infection. These tests will involve experimental infections using appropriate human Hp strains of mouse lines that differ markedly in inflammatory responses (e.g., IL-10 and IL-12 knockout), and also gerbils, a more permissive host. Collectively, the proposed studies will increase understanding of Hp infection mechanisms and associated disease, and perhaps of who to treat for infection and how such treatment can be most effective.